This invention relates to axial split-pin tumbler-type lock mechanisms having structure designed to render them resistant to picking.
In general, the axial split-pin tumbler-type lock mechanisms include a rotatable operating part and a stationary part, which adjoin at an interfacial plane. Tumblers each including a driver element and a follower element are mounted in bores in the parts which meet in alignment at the interfacial plane, and the tumblers are movable back and forth in the bores. When the joints between the tumbler elements coincide with the interfacial plane upon insertion of the proper key, the operating part may be rotated by means of the key, to accomplish a desired function. Illustrative of the lock mechanisms to which the present invention is directed are Kerr U.S. Pat. No. 3,541,819, Kerr U.S. Pat. No. 3,813,906, and Steinbach U.S. Pat. No. 3,916,657.
As disclosed in U.S. Pat. No. 3,541,819, the lock mechanisms of the foregoing type have in the past been picked, embodying what may be referred to as a "gang pick," of the type disclosed in the patent. In use, the pick is applied to the lock mechanism, a rotational torque or bias is applied to the operating part thereby, to displace the operating part to a slight extent relative to the stationary part, and a jiggling motion is utilized to work the tumbler elements from rear to front and catch them at the interfacial plane, on the margins of tumbler bores which project over adjacent bores. When an element of each of the tumblers has been caught at the interfacial plane in such manner, the operating part is free to rotate and the lock mechanism is in an unlocked condition. In another type of picking tool, the tumblers are picked individually, and the tumbler elements are worked from front to rear. Numerous improvements have been devised to increase the pick resistance of lock mechanisms such as those illustrated by the foregoing patents, and they have met with varying degrees of success.